A stepping motor is typically configured of a rotor fixed to the rotating drive shaft of the motor, and a stator mounted around the rotor. The motor driver for driving the stepping motor can drive the rotor in a forward rotation in fixed angular increments by sequentially applying electric current corresponding to the excitation phase to coils wound about the stator. The excitation phase specifies how the motor driver supplies electric current to the coils in the stepping motor. The rotational position of the stepping motor (rotor position) is therefore determined according to this excitation phase.
The motor drivers used to drive stepping motors come in two types: a clock input type and a parallel input type. This is described in United States Patent Application Publication No. 2008/0019677A1, for example.
A control unit, configured of a CPU, ASIC, or the like, is configured to update the excitation phase and to supply the motor driver of the parallel input type with those control signals that are indicative of the polarity and the amount of the current that should be supplied to the coils to attain the updated excitation phase. The motor driver drives the stepping motor by supplying the coils with the current whose polarity and amount are determined by the control signals.
Contrarily, the control unit supplies the motor driver of the clock input type with: a clock signal indicating the timing for switching the excitation phase; an excitation mode signal indicating the excitation mode for the motor; and a rotating direction signal indicating the direction in which the motor should be rotated. The motor driver updates the excitation phase based on the received signals, and drives the stepping motor by supplying the coils with the current whose polarity and amount are determined by the updated excitation phase.
There has been proposed a recording device which employs a stepping motor and whose control unit stores data of the final excitation phase of the stepping motor at the time the recording device enters a sleep mode to halt the motor. When the recording device is awakened from the sleep mode, the control unit reads the data of the final excitation phase, and resumes driving the stepping motor via a motor driver based on the read data of the final excitation phase. This conventional recording device is described in U.S. Pat. No. 6,963,415B1.